Refs #969 - Proxy-side changes for serving templates from the proxy

An update to @GregSutcliffe's original PR (https://github.com/theforeman/smart-proxy/pull/100/files). Ports his original feature to the new plugin api.
This doesn't work, i get host as `nil`. If i add logging of the uri object to request_factory.create_request I get:
```
I, [2014-10-29T17:18:52.945476 #12172]  INFO -- : uri.scheme = 
I, [2014-10-29T17:18:52.945558 #12172]  INFO -- : uri.host   = 
I, [2014-10-29T17:18:52.945635 #12172]  INFO -- : uri.port   = 
I, [2014-10-29T17:18:52.945752 #12172]  INFO -- : uri.path   = /unattended/provision
```
Not good. I tried changing this line to `"#{Proxy::Templates::Plugin.settings.foreman_url}/unattended/#{kind}"` which correctly gave:
```
I, [2014-10-29T17:20:05.681750 #12604]  INFO -- : uri.scheme = http
I, [2014-10-29T17:20:05.681812 #12604]  INFO -- : uri.host   = 192.168.122.1
I, [2014-10-29T17:20:05.681878 #12604]  INFO -- : uri.port   = 3000
I, [2014-10-29T17:20:05.681934 #12604]  INFO -- : uri.path   = /unattended/provision
```
but i'm still getting connection refused. Foreman is definitely listening on 192.168.122.1:3000 - investigating the connection refused now.